First of all, try using another encoder rather than ac3
. With your command, you're basically letting avconv
decide on everything by its own. While this may be a bug (please file a report if it works in FFmpeg), you can probably circumvent it by specifying an encoder — I'd suggest MP3 if you have that linked to libav:
avconv -i 1.mkv -c:a libmp3lame ./converted/1.avi
Here's an indication for the error:
Incompatible sample format 's16' for codec 'ac3'
Maybe try forcing AC3 and maybe even specifying parameters like -b:a
:
avconv -i 1.mkv -c:a ac3 ./converted/1.avi
You might also want to use proper options for the video stream too, rather than converting a (probably high quality) h.264 stream to plain MPEG-4. I'm pretty sure the result of your conversion will look bad if you don't.